At present, graphene fiber materials, as a preferred material for fabricating flexible electronic devices, have attracted the attention of researchers, and have great potential in the fields of flexible energy storage devices and intelligent sensor devices. However, due to the serious stacking of graphene sheets and their natural hydrophobicity, the specific surface area of graphene sheets is small and the affinity with electrolyte is not good, which greatly limits the excellent theoretical electrochemical properties of graphene in macro materials.

  To this end, Professor Zhu Meifang's team has developed a non-liquid crystal spinning method for graphene solution in the previous research work. By adjusting the charged surface of graphene lamellae in solution with alkali solution, strong electrostatic repulsion force is generated between the lamellae, resulting in disordered arrangement. Porous pure graphene fibers (Nano Energy, 2015, 15, 64) with high electrochemical properties are continuously prepared on a large scale. 2) and made a series of research progress. Through this method, our team obtained polyvinyl alcohol/graphene hybrid fibers (Journal of Power Sources, 2016, 319, 271) with high strength, high hydrophilicity and high electrochemical properties. We further prepared hybrid graphene fibers (Journal of Power Sources, 2016, 306, 481; Carbon, 2017, 113, 151) with high electrochemical properties by using inorganic nanoparticles (such as MnO 2, MoO 3) with pseudocapacitive properties as nanoactive components through multi-component hybrid assembly.

 Recently, on the basis of our previous work, our team used cellulose nanocrystals as nano-reinforcement units, which have one-dimensional rod-like rigid structure and rich hydrophilic groups on the surface. Through the above-mentioned spinning method, combined with chemical reduction, multicomponent heterogeneously assembled rGO/CNC hybrid fibers were obtained. The results show that the graphene hybrid fibers obtained by this strategy have many advantages. Firstly, the nanorod-like morphology of CNC can not only form intercalation structure with graphene lamellae, improve the serious accumulation of graphene lamellae in graphene fibers, but also inhibit the bending and folding of graphene lamellae in the process of fiber forming and make them align in the fiber axis. As a result, ordered nanoporous structure (shown in Fig. 1a) can be formed to provide unobstructed nanochannels for electrolyte transport. Secondly, due to its rigid structure, CNC will not form a state like polymer chain coating on the surface of graphene lamellae, while enhancing its performance, maintaining the effective connection of graphene lamellae along the fiber axis to ensure high hybrid graphene fibers. Conductivity (shown in Fig. 1b); Thirdly, the abundant hydrophilic groups on CNC surface can not only form a strong hydrogen bond network with the residual oxygen-containing functional groups (hydroxyl, carboxyl, carbon, etc.) on the surface of graphene lamellae, which can effectively enhance their mechanical properties (shown in Fig. 1c), but also give graphene high hydrophilicity (shown in Fig. 1d) by hydrophilic nanounits, which can effectively improve fibers and graphene. Affinity of electrolyte solution.

Fig1. Cross section electron microscopy (a), electrical conductivity (b), mechanical properties (c) and hydrophilicity (d) of hybrid graphene fibers

  Subsequently, we assembled the hybrid graphene fibers into supercapacitors, and found that the hybrid graphene fibers have excellent electrochemical performance, excellent series-parallel connection and flexibility (as shown in Figure 2a-b), and have relatively high energy density and power density in similar supercapacitors (as shown in Figure 2c). Therefore, the above research shows that the hybrid graphene fiber as a flexible electrode material has broad application prospects in wearable electronic devices, especially in the field of flexible supercapacitors. This achievement was recently published in Carbon.

Figure 2. Series-parallel property (a), bending test (b) and Ragone diagram (c) of supercapacitors prepared from hybrid graphene fibers

The author of this paper is：Guoyin Chen, Tao Chen, Kai Hou, Wujun Ma, Mike Tebyetekerwa, Yanhua Cheng, Wei Weng, Meifang Zhu